[from Mary Powers 940720 8:45]
Paul George:
Sometimes the magnitude or rate of change of the error signal
may be sufficient. i guess it depends on how sophisticated you
allow the output function (F2) to be. if it can select between
different actions based upon threshholds for the error signal,
fine. the idea is that different actions may be required in
response to different amounts or rates of disturbance. to deal
with a punch, sometimes you block, sometimes you duck. Depends
on how fast it is coming, and where your arms are.
I think the more common structure might be having another
control loop monitoring the error signal, treating it as a
controlled variable. that loop's output function would then
activate the appropriate loop for the needed kind of action
(i.e. an 'emergency' loop. this presupposes that you have
multiple loops capable of controlling the same perception, but
have their reference variables adjusted so only one actually
generates an error signal at a given time. Possible?
Possible, maybe, if you are designing such a system. But remember
PCT is under the constraint of being neurologically plausible,
and also under the constraint of keeping things as simple as
possible unless evidence demands otherwise. Therefore the output
is not allowed to be very sophisticated.
Part of the problem here is that you are looking at the
canonical, single loop model, and trying to see how it can do the
work of what PCT conceives of as a hierarchical arrangement of a
multitude of control systems, none of which is engaged in
monitoring the size of the error signal (aside from the
postulated reorganization function which has as input a state of
large and chronic error).
In PCT, error signals are outputs to lower levels, where they
function as reference signals. Only at the lowest level is output
a signal for muscles to contract. There is no function selecting
actions: the actions are dependent on numerous output signals to
various muscles, which in turn are dependent on the comparison of
the desired state of affairs to the perceived environmental
situation. In the case of ducking or blocking a punch, the state
of the environment is the perception of how fast the punch is
coming, PLUS, as you correctly pointed out, where your arms are -
which is as much a part of the environment of the system as the
approaching punch. If your arms are in a particular place, you've
got to duck because it's too late to block, etc.
In the heat of a fight, this is all going on at pretty low
levels, and your success at blocking or ducking is not a high-
level intellectual exercise - it's a matter of much practice and
training to have lower-level loops - perceptions, comparison,
outputs - be sufficient and correct; for the lower systems to
duck rather than block because of experience with what can be
done or not done when the arms are in various positions. The same
applies to dealing with braking in emergencies. Hitting the
brakes hard, which in normal situations is the right thing to do,
is a poor idea on an icy slope, which is why incomers from Texas
and California end up in ditches around here in the wintertime
more often than the natives.
ยทยทยท
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Sometimes the magnitude or rate of change of the error signal
may be sufficient. i guess it depends on how sophisticated you
allow the output function (F2) to be. if it can select between
different actions based upon threshholds for the error signal,
fine. the idea is that different actions may be required in
response to different amounts or rates of disturbance. to deal
with a punch, sometimes you block, sometimes you duck. Depends
on how fast it is coming, and where your arms are.
I think the more common structure might be having another
control loop monitoring the error signal, treating it as a
controlled variable. that loop's output function would then
activate the appropriate loop for the needed kind of action
(i.e. an 'emergency' loop. this presupposes that you have
multiple loops capable of controlling the same perception, but
have their reference variables adjusted so only one actually
generates an error signal at a given time. Possible?
Possible, maybe, if you are designing such a system. But remember
PCT is under the constraint of being neurologically plausible,
and also under the constraint of keeping things as simple as
possible unless evidence demands otherwise. Therefore the output
is not allowed to be very sophisticated.
Part of the problem here is that you are looking at the
canonical, single loop model, and trying to see how it can do the
work of what PCT conceives of as a hierarchical arrangement of a
multitude of control systems, none of which is engaged in
monitoring the size of the error signal (aside from the
postulated reorganization function which has as input a state of
large and chronic error).
In PCT, error signals are outputs to lower levels, where they
function as reference signals. Only at the lowest level is output
a signal for muscles to contract. There is no function selecting
actions: the actions are dependent on numerous output signals to
various muscles, which in turn are dependent on the comparison of
the desired state of affairs to the perceived environmental
situation. In the case of ducking or blocking a punch, the state
of the environment is the perception of how fast the punch is
coming, PLUS, as you correctly pointed out, where your arms are -
which is as much a part of the environment of the system as the
approaching punch. If your arms are in a particular place, you've
got to duck because it's too late to block, etc.
In the heat of a fight, this is all going on at pretty low
levels, and your success at blocking or ducking is not a high-
level intellectual exercise - it's a matter of much practice and
training to have lower-level loops - perceptions, comparison,
outputs - be sufficient and correct; for the lower systems to
duck rather than block because of experience with what can be
done or not done when the arms are in various positions. The same
applies to dealing with braking in emergencies. Hitting the
brakes hard, which in normal situations is the right thing to do,
is a poor idea on an icy slope, which is why incomers from Texas
and California end up in ditches around here in the wintertime
more often than the natives.
Mary P.